Cross-section processing-and-observation method and cross-section processing-and-observation apparatus

ABSTRACT

A cross-section processing-and-observation method, including a cross-section exposure step in which a sample is irradiated with a focused ion beam to expose a cross-section of the sample, and a cross-sectional image acquisition step in which the cross-section is irradiated with an electron beam to acquire a cross-sectional image of the cross-section. The cross-section exposure step and the cross-sectional image acquisition step are repeatedly performed along a predetermined direction of the sample at a setting interval to acquire multiple cross-sectional images of the sample. The method also includes a specific observation target detection step in which a predetermined specific observation target from the cross-sectional image acquired a the cross-sectional image acquisition step is detected. In the specific observation target detection step, after a predetermined specific observation target is detected, the setting interval of the cross-section exposure step is set to be shorter than that before the specific observation target is detected.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority ofJapanese Patent Application No. 2013-182586 filed on Sep. 3, 2013, thecontents of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a cross-sectionprocessing-and-observation method and a cross-sectionprocessing-and-observation apparatus, in which a cross-section of asample, which is formed by a focused ion beam, is irradiated with anelectron beam to obtain a cross-sectional image of the sample.

For example, as a method of analyzing an internal structure of a samplesuch as a semiconductor device or performing a three-dimensionalobservation thereof, a cross-section processing-and-observation methodis known, the method including: scanning an electron beam (EB) using ascanning electron microscope (SEM) to acquire plural cross-sectionalimages of the sample while repeatedly performing cross-sectionprocessing (etching processing) using a focused ion beam (FIB); andcombining the plural cross-sectional images to construct athree-dimensional image of the sample (for example, JP-A-2008-270073).

This cross-section processing-and-observation method is a method called“Cut&See” in which a composite charged particle beam device is used, andhas an advantageous effect compared to other methods in that across-sectional image of a sample can be seen and the inside of thesample can be three-dimensionally observed from various directions.

As a specific example, a sample is irradiated with an FIB to etch thesample such that a cross-section of the sample is exposed. Next, theexposed cross-section is observed with a SEM to acquire across-sectional image. Next, the sample is etched again to expose thenext cross-section, and a second cross-sectional image is acquired bythe SEM observation. By repeating the etching processing and the SEMobservation in this way along an arbitrary direction of the sample,plural cross-sectional images are acquired. Lastly, by combining theacquired plural cross-sectional images, a three-dimensional imagethrough which the inside of the sample can be seen is constructed.

In recent years, a device pattern has become minute due to densitygrowth or reduction in size of a semiconductor device. Therefore, in thecross-section processing-and-observation, it is required that a moreminute observation target can be observed with a higher resolution thanin the past. In order to perform cross-sectionprocessing-and-observation of a sample including a minute observationtarget, it is necessary that a high-density cross-sectional image beacquired to enhance the resolution of the cross-sectional image.

However, when an attempt to enhance the resolution of a cross-sectionalimage is made in the cross-section processing-and-observation, there isa problem in that the time required to obtain a cross-sectional imageincreases and the time required to construct a three-dimensional imageof one sample increases significantly. Therefore, a cross-sectionprocessing-and-observation method and a cross-sectionprocessing-and-observation apparatus which are capable of constructing ahigh-resolution three-dimensional image of a sample including a minuteobservation target within a short period of time are required.

An aspect of the present invention has been made in consideration of theabove-described circumstances, and an object thereof is to provide across-section processing-and-observation method and a cross-sectionprocessing-and-observation apparatus which are capable of obtainingplural cross-sectional images of a minute observation target with a highresolution within a short period of time.

SUMMARY OF THE INVENTION

In order to solve the above-described problems, according to aspects ofthe present invention, a cross-section processing-and-observation methodand a cross-section processing-and-observation apparatus which aredescribed below are provided.

That is, according to an aspect of the present invention, there isprovided a cross-section processing-and-observation method including: across-section exposure step of irradiating a focused a sample with ionbeam to expose a cross-section of the sample; a cross-sectional imageacquisition step of irradiating the cross-section with an electron beamto acquire a cross-sectional image of the cross-section; and a step ofrepeatedly performing the cross-section exposure step and thecross-sectional image acquisition step along a predetermined directionof the sample at a setting interval to acquire plural cross-sectionalimages of the sample, in which in the cross-sectional image acquisitionstep, a cross-sectional image is acquired under different conditionsettings for plural regions of the cross-section. As a result, forexample, when a region including the entire portion of a cross-sectionand a region including only a part of the inside of the cross-sectionare observed as plural regions of the cross-section, cross-sectionalimages of the respective regions can be observed under differentcondition settings. In this way, only a desired region can beefficiently observed, and information of a cross-section can be acquiredin more detail.

In the above-described cross-section processing-and-observation method,conditions of the cross-sectional image acquisition step may include atleast one of an accelerating voltage of the electron beam, a currentvalue of the electron beam, an aperture value of an object lens, anastigmatism correction amount, a brightness, a contrast, amagnification, an imaging time of the cross-sectional image, the numberof times of acquiring a cross-sectional image for each cross-section, apixel size, and a detector used for acquiring an cross-sectional image.The pixel described here refers to a unit pixel of a cross-sectionalimage.

In the above-described cross-section processing-and-observation method,the setting interval may be equal to or an integer multiple of a pixelsize of any one of the plurality of regions, or the pixel size may be aninteger multiple of the setting interval. As a result, when athree-dimensional image is constructed, a relationship between a pixelof a cross-section and a slice interval, that is, the size of a voxelwhich is a pixel of the three-dimensional image is clarified. Therefore,the three-dimensional image is visually easily recognized.

The above-described cross-section processing-and-observation method mayfurther include a specific observation target detection step ofdetecting a predetermined specific observation target, in which in thespecific observation target detection step, after a predeterminedspecific observation target is detected, a condition setting of thecross-section exposure step and a condition setting of thecross-sectional image acquisition step may be updated.

In the above-described cross-section processing-and-observation method,when the conditions of the cross-section exposure step are updated, thesetting interval may be set to be shorter than that before the specificobservation target is detected.

In the above-described cross-section processing-and-observation method,plural types of the specific observation targets may be set, anddifferent condition settings of the cross-section exposure step anddifferent condition settings of the cross-sectional image acquisitionstep may be set for individual regions where the respective specificobservation targets are detected.

In the above-described cross-section processing-and-observation method,when the condition setting of the cross-section exposure step and thecondition setting of the cross-sectional image acquisition step are set,the setting interval may be equal to or an integer multiple of a pixelsize of the cross-sectional image.

In the above-described cross-section processing-and-observation method,in the specific observation target detection step, an EDS measurement oran EBSD measurement of the cross-section may be performed.

In the above-described cross-section processing-and-observation method,in the specific observation target detection step, a contrast change ofa cross-sectional image obtained in the cross-sectional imageacquisition step may be observed.

In the above-described cross-section processing-and-observation method,the conditions of the cross-section exposure step may include at leastone of an accelerating voltage of the focused ion beam, a current valueof the focused ion beam, an irradiation range of the focused ion beam inthe sample, and a visual field range of the focused ion beam.

In the above-described cross-section processing-and-observation method,the specific observation target detection step may be performed oncewhile the cross-sectional image acquisition step is performed multipletimes.

In the above-described cross-section processing-and-observation method,in the specific observation target detection step performed after thespecific observation target is detected, cross-sectionprocessing-and-observation may not be performed on other portions of thesample when the specific observation target is not detected anymore.

The above-described cross-section processing-and-observation method mayfurther include a step of forming a correction mark by irradiation ofthe focused ion beam, in which in the cross-section exposure step, animage of the correction mark may be acquired with a higher magnificationthan the visual field range of the focused ion beam among the conditionsof the cross-section exposure step.

The above-described cross-section processing-and-observation method mayfurther include a step of forming a correction mark by irradiation ofthe focused ion beam, in which in the cross-sectional image acquisitionstep, when the cross-sectional image is acquired, an image of thecorrection mark may be acquired at the same time with a highermagnification than the magnification of a cross-section observationregion observed by the electron beam among the conditions of thecross-sectional image acquisition step.

According to another aspect of the present invention, there is provideda cross-section processing-and-observation apparatus including: a samplestage on which a sample is placed; a focused ion beam column thatirradiates the sample with a focused ion beam; an electron beam columnthat irradiates the sample with an electron beam; a secondary electrondetector or backscattered electron detector that detects secondaryelectrons or backscattered electrons generated from the sample; and acontrol unit that repeatedly performs a cross-section exposure step, inwhich the sample is irradiated with a focused ion beam to expose across-section of the sample, and a cross-sectional image acquisitionstep, in which the cross-section is irradiated with an electron beam toacquire a cross-sectional image of the cross-section, along apredetermined direction of the sample at a setting interval to acquire across-sectional image under different conditions for plural regions ofthe cross-section in the cross-sectional image acquisition step.

In the above-described cross-section processing-and-observationapparatus, the control unit may control the setting interval to be equalto or an integer multiple of a pixel size of any one of the plurality ofregions or may control the pixel size to be an integer multiple of thesetting interval.

In the above-described cross-section processing-and-observation method,in a specific observation target detection step of detecting apredetermined specific observation target, after the predeterminedspecific observation target is detected, the control unit may updateconditions of the cross-section exposure step and conditions of thecross-sectional image acquisition step.

According to the present invention, since only a desired minute regionis observed with a high resolution, a cross-sectional image can beacquired within a short period of time. As a result, a high-resolutionthree-dimensional image including a desired observation target can beconstructed within a short period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram illustrating a cross-sectionprocessing-and-observation apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram illustrating a configurationof a control unit of the cross-section processing-and-observationapparatus.

FIGS. 3A to 3C are diagrams illustrating a state where cross-sectionprocessing-and-observation of a semiconductor wafer is performed.

FIG. 4 is a diagram illustrating a cross-sectionprocessing-and-observation method according to a first embodiment of thepresent invention.

FIG. 5 is a schematic diagram illustrating observation images ofcross-sections.

FIG. 6 is a diagram illustrating an observation image of a correctionpattern.

FIG. 7 is a diagram illustrating the cross-sectionprocessing-and-observation method according to the first embodiment

FIG. 8 is a diagram illustrating the cross-sectionprocessing-and-observation method according to the first embodiment.

FIGS. 9A and 9B are diagrams illustrating the cross-sectionprocessing-and-observation method according to the first embodiment.

FIG. 10 is a schematic diagram illustrating an example of athree-dimensional image which is constructed using the cross-sectionprocessing-and-observation method according to the present invention.

FIG. 11 is a flowchart illustrating a cross-sectionprocessing-and-observation method according to a second embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a cross-section processing-and-observation method and across-section processing-and-observation apparatus according to theillustrative embodiment will be described. Respective illustrativeembodiments described below are specific examples for easilyunderstanding the scope of the present invention and do not limit thepresent invention unless specified otherwise. In addition, in thedrawings used in the following description, major components may beenlarged and illustrated in order to make characteristics of the presentinvention easier to understand, and a dimensional ratio of eachcomponent may not be the same as that of the actual one.

(Cross-Section Processing-and-Observation Apparatus)

FIG. 1 is a schematic configuration diagram illustrating a cross-sectionprocessing-and-observation apparatus. A cross-sectionprocessing-and-observation apparatus 10 according to the illustrativeembodiment includes a focused ion beam (FIB) column 11, an electron beam(EB) column 12, and a sample chamber 13. The focused ion beam column 11and the electron beam column 12 are accommodated in the sample chamber13 and are arranged therein so as to irradiate a sample S placed on astage (sample stage) 14 with a focused ion beam (FIB) and an electronbeam (EB). The stage 14 can move, tilt and rotate in any of X, Y, and Zdirections so as to be able to adjust the sample S in an arbitrarydirection.

It is preferable that the focused ion beam (FIB) column 11 and theelectron beam (EB) column 12 be arranged such that beams emitted fromthe respective columns are respectively perpendicular to the sample S.This is because an electron beam can be emitted in a directionperpendicular to a processed cross-section, and a high-resolutioncross-sectional image can be acquired.

The cross-section processing-and-observation apparatus 10 furtherincludes a focused ion beam (FIB) control unit 15 and an electron beam(EB) control unit 16. The focused ion beam control unit 15 controls thefocused ion beam column 11 and emits a focused ion beam at an arbitrarytime. The electron beam control unit 16 controls the electron beamcolumn 12 and emits an electron beam at an arbitrary time.

The cross-section processing-and-observation apparatus 10 furtherincludes a secondary electron detector 17 and an EDS detector 18. Thesecondary electron detector 17 irradiates the sample S with a focusedion beam 21 or an electron beam 22 and detects secondary electronsgenerated from the sample S. In addition, the EDS detector 18 irradiatesthe sample S with the electron beam 22 and detects an X-ray generatedfrom the sample S. The X-ray generated from the sample S includes acharacteristic X-ray unique to a material included in the sample S. Thematerial included in the sample S can be specified based on thecharacteristic X-ray.

Instead of the secondary electron detector 17, a backscattered electrondetector is also preferably provided. The backscattered electrondetector detects backscattered electrons obtained by the electron beambeing backscattered from the sample S. A cross-sectional image can beacquired from these backscattered ions.

In addition, instead of the EDS detector 18, an EBSD detector is alsopreferably provided. In the EBSD detector, when a crystalline materialis irradiated with an electron beam, a diffraction pattern, that is, anEBSD pattern is observed by electron backscatter diffraction occurringon the surface of the sample S, and information pertaining to thecrystal system or crystal orientation of the sample S is obtained. Bymeasuring and analyzing such an EBSD pattern, information pertaining tothe distribution of the crystal system or crystal orientation of aminute region of the sample S can be obtained, and a material includedin the sample S can be specified.

Further, instead of using the EDS detector 18, a configuration may beadopted in which a specific observation target is detected by comparingthe contrast of an observation image, which is obtained in an imageforming unit 23 described below, to the contrast of, for example, areference image which is stored in advance.

The cross-section processing-and-observation apparatus 10 furtherincludes an image forming unit 23 that forms an observation image of across-section of the sample S and a display unit 24 that displays theobservation image. The image forming unit 23 forms a SIM image based ona signal for scanning the focused ion beam 21 and a signal of thesecondary electrons detected by the secondary electron detector 17. Thedisplay unit 24 displays the SIM image obtained by the image formingunit 23. The display unit 24 may be configured of, for example, adisplay apparatus.

In addition, the image forming unit 23 forms a SEM image based on asignal for scanning the electron beam 22 and the signal of the secondaryelectrons detected by the secondary electron detector 17. The displayunit 24 displays the SEM image obtained by the image forming unit 23. Inaddition, the image forming unit 23 forms an EDS map based on the signalfor scanning the electron beam 22 and a signal of the characteristicsX-ray detected by the EDS detector 18. The display unit 24 displays theEDS map obtained by the image forming unit 23. The EDS map specifies amaterial of the sample S at each electron beam irradiation point fromenergy of the detected characteristic X-ray, and shows distribution ofmaterial in an irradiation region of the electron beam 22.

The cross-section processing-and-observation apparatus 10 furtherincludes a control unit 25 and an input unit 26. An operator inputsvarious control conditions of the cross-sectionprocessing-and-observation apparatus 10 through the input unit 26. Theinput unit 26 transmits the input information to the control unit 25.The control unit 25 outputs control signals to the focused ion beamcontrol unit 15, the electron beam control unit 16, and the imageforming unit 23, and controls the overall operation of the cross-sectionprocessing-and-observation apparatus 10.

In the cross-section processing-and-observation apparatus 10, it ispreferable that a source gas supply mechanism be further formed to forma deposition film for protecting the surface of the sample S. Thedeposition film for protecting the surface of the sample S is formedthrough the source gas supply mechanism. On the deposition film, acorrection mark which is a positioning index for combining pluralcross-sectional images can be formed, for example, in a step of forminga three-dimensional image of the sample S described below. Thecorrection mark is the linear index that extends along a direction(hereinafter, referred to as “predetermined direction”) in which thedeposition film is irradiated with the focused ion beam 21 tosequentially slice the sample S.

FIG. 2 is a schematic configuration diagram illustrating a configurationof a control unit of the cross-section processing-and-observationapparatus.

The control unit 25 includes a processing condition storage unit 31, anobservation condition storage unit 32, a cross-sectionprocessing-and-observation control unit 33, a specific material storageunit 34, an observation image storage unit 35, a specific materialdetermination unit 36, and a three-dimensional image construction unit37.

The processing condition storage unit 31 stores a setting value of aslicing interval of the sample S and setting values of the position andsize of a processing region of the focused ion beam 21 in the sample S.The processing condition storage unit 31 stores: a slicing interval(hereinafter, referred to as “high-speed processing interval”) which isset when one or plural types of preset specific observation targets arenot detected in the sample S; and a slicing interval (hereinafter,referred to as “precise processing interval”) which is narrower than thehigh-speed processing interval and is set when the specific observationtargets are detected in the sample S. It is preferable that pluralsetting values corresponding to the sizes and types of the specificobservation targets be stored as the precise processing interval.

In addition, the processing condition storage unit 31 stores: a settingvalue of the size of a processing region of the sample S which is setwhen the processing region is sliced at the high-speed processinginterval; and a setting value of the size of a processing region of thesample S which is set when the processing region is sliced at theprecise processing interval.

In addition, the processing condition storage unit 31 stores settingvalues of an accelerating voltage and a current of the focused ion beam21. When the focused ion beam 21 which is accelerated at a lowaccelerating voltage is used, a damage layer formed on the sample S canbe reduced. In addition, when the focused ion beam 21 having a lowcurrent is used, the width of a beam shape is narrow. Therefore, a steepcross-section can be formed, which is preferable, particularly, when aminute observation target is processed. Accordingly, the processingcondition storage unit 31 stores a setting value of a high current forslicing at the high-speed processing interval and a setting value of alow current for slicing at the precise processing interval. It ispreferable that setting values of a low current having the numbercorresponding to the types of the precise processing interval be set.

The observation condition storage unit 32 stores setting values of theposition and size of an observation region of the sample S and settingvalues of an accelerating voltage and a current of the electron beam 22.When the electron beam 22 which is accelerated at a low acceleratingvoltage is used, the penetration length of the electron beam 22 throughthe sample S is short. Therefore, an observation image on which onlyinformation of the vicinity of a cross-section is reflected can beacquired. In addition, when the electron beam 22 having a low current isused, the width of a beam shape is narrow, and thus a high-resolutionobservation image can be acquired. Therefore, it is preferable that theelectron beam 22 having a low current be used when a minute observationtarget is observed.

On the other hand, when the accelerating voltage of the electron beam 22is high, the penetration length of the electron beam 22 through thesample S increases. Therefore, an observation image on which informationof the inside of the sample S is reflected can be acquired, and a minuteobservation target is easily detected. Accordingly, the observationcondition storage unit 32 stores: setting values of a high acceleratingvoltage and a high current which are set to perform cross-sectionobservation for detecting a large observation target and a minuteobservation target; and setting values of a low accelerating voltage anda low current which are set to observe a minute observation target. Itis preferable that plural setting values corresponding to the sizes andtypes of the preset specific observation targets be set as the settingvalues of a low accelerating voltage and a low current which are set toobserve a minute observation.

The observation condition storage unit 32 further stores an aperturevalue of an object lens of the electron beam column 12, an astigmatismcorrection amount, a brightness, a contrast, a magnification, an imagingtime of an observation image (cross-sectional image) of the sample S,the number of times of acquiring an observation image, a pixel size, andthe like.

In addition, the observation condition storage unit 32 stores varioustypes of observation images. The types of observation images include aSEM image, a backscattered electron image, a SIM image, and an EDSimage. When the SEM image and the SIM image are acquired, the secondaryelectrons are detected by the secondary electron detector 17, and theSEM image and the SIM image are formed by the image forming unit 23.When the EDS image is acquired, the characteristic X-ray is detected bythe EDS detector 18, and the EDS map is formed by the image forming unit23. In addition, when the backscattered electron image is acquired, thebackscattered electrons are detected by the backscattered electrondetector inside the electron beam column 12, and the backscatteredelectron image is formed by the image forming unit 23.

The specific material storage unit 34 stores an element of the materialincluded in the specific observation target. When the element isdetected by the EDS measurement in the cross-sectionprocessing-and-observation for detecting a minute observation target,conditions of the cross-section processing-and-observation, that is,conditions of a cross-section exposure step and conditions of across-sectional image acquisition step are updated. The cross-sectionexposure step and the cross-sectional image acquisition step will bedescribed below.

When an operator inputs the above-described respective setting valuesand the element of the material included in the specific observationtarget through the input unit 26, the respective storage units of thecross-section processing-and-observation apparatus 10 stores the settingvalues and the element. The stored setting values of the processingconditions and the observation conditions are read by the cross-sectionprocessing-and-observation control unit 33. In addition, the element ofthe specific observation target is output from the specific materialdetermination unit 36.

The cross-section processing-and-observation control unit 33 outputsirradiation conditions of the focused ion beam 21, that is, processingconditions of the sample S to the focused ion beam column 11. As aresult, the focused ion beam column 11 irradiates the sample S with thefocused ion beam 21 to etch the sample in a predetermined shape suchthat a cross-section at an arbitrary position is exposed.

The cross-section processing-and-observation control unit 33 outputsirradiation conditions of the electron beam 22, that is, processingconditions of the sample S to electron beam column 12. The electron beamcolumn 12 irradiates the sample S with the electron beam 22 andacquires, for example, an observation image of the sample S fromsecondary electrons or an X-ray generated from a cross-section of thesample S which is formed by the focused ion beam 21.

According to the type of an observation image to be acquired, thecross-section processing-and-observation control unit 33 controls thesecondary electron detector 17, the backscattered electron detector, orthe EDS detector 18 to detect the secondary electrons, the backscatteredelectrons, or the characteristic X-ray generated from the sample S.Based on the detected secondary electrons, backscattered electrons, orcharacteristic X-ray, an observation image is formed by the imageforming unit 23.

The observation image storage unit 35 stores the observation imageformed by the image forming unit 23. The display unit 24 displays theobservation image stored in the observation image storage unit 35.Further, when a three-dimensional image described below is constructedfrom the obtained plural observation images, the three-dimensional imageconstruction unit 37 sequentially reads the plural observation imagesstored in the observation image storage unit 35 to construct thethree-dimensional image. This three-dimensional image is displayed bythe display unit 24.

The specific material determination unit 36 reads the element of thematerial, which is included in the previously stored specificobservation target, from the specific material storage unit 34 duringthe execution of the cross-section processing-and-observation and readsthe EDS map, which is acquired in the cross-sectionprocessing-and-observation, from the observation image storage unit 35.When the element appears on the EDS map, that is, when the specificobservation target is detected, the specific material determination unit36 transmits a signal to the cross-section processing-and-observationcontrol unit 33. After the cross-section processing-and-observationcontrol unit 33 receives the signal, a condition setting of thecross-section exposure step and a condition setting of thecross-sectional image acquisition step are updated.

(Summary of Cross-Section Processing-and-Observation Method)

The summary of a cross-section processing-and-observation method inwhich the cross-section processing-and-observation apparatus having theabove-described configurations is used will be described. Here, forexample, a case where a semiconductor wafer is used as a sample of anobservation target will be described as an example. FIGS. 3A to 3C arediagrams illustrating a state where cross-sectionprocessing-and-observation of a semiconductor wafer is performed. FIG.3A illustrates a processing groove of the semiconductor wafer. FIG. 3Bis an enlarged view illustrating the periphery of the processing groove.FIG. 3C is a cross-sectional view taken along line A-A of FIG. 3B. Thesample (semiconductor wafer) S has a minute device structure therein. Inthe cross-section processing-and-observation, cross-sectionalobservation images of desired observation targets such as a devicestructure and defects inside the sample S are acquired and analyzed.When the observation target is minute, it is difficult to accuratelydetect a position thereof in the sample S due to the positioningaccuracy of the stage and the accuracy of device processing.

Accordingly, the focused ion beam 21 is emitted in the vicinity of aposition where the observation target is assumed to be present to form aprocessing groove 41 by etching. A processing region of thecross-section processing is set such that the processing groove 41 iswidened to the position where the observation target is assumed to bepresent. In the following description, a direction in which theprocessing groove 41 is widened to the position where the observationtarget is assumed to be present will be referred to as “predetermineddirection (processing progression direction) PD”.

As the processing groove 41 to be formed on the sample (semiconductorwafer) S, a slope shape whose depth from the surface of the sample Sgradually increases toward the predetermined direction PD is formed inadvance such that the electron beam 22 can be emitted onto a formedcross-section (observation surface) 41 s. The processing groove 41 iswidened along the predetermined direction PD in order of processingregions 42, 43, 44, . . . of slicing from the cross-section 41 s.Whenever the processing of each of the processing regions 42, 43, 44, .. . is completed, the electron beam 22 is emitted onto a rectangularcross-section (observation surface), which is exposed by the processingalong the thickness direction of the sample S, to acquire an observationimage. In addition, the EDS map is also acquired from all thecross-sections or after several times or several tens of times ofprocessing.

A slicing interval (setting interval) D of slicing of each of theprocessing regions 42, 43, 44, . . . is updated before and after thepreset specific observation target is detected. For example, when thespecific observation target is detected, the slicing interval D isupdated to be narrower than that before the detection. This update ofthe slicing interval D is performed by updating the conditions of thecross-section exposure step.

In addition, conditions of acquiring an observation image of eachcross-section after the completion of slicing of each of the processingregions 42, 43, 44, . . . are updated before and after the presetspecific observation target is detected. This update of the conditionsof acquiring an observation image of each cross-section is performed byupdating the condition setting of the cross-sectional image acquisitionstep. The conditions of the cross-section exposure step and theconditions of the cross-sectional image acquisition step will bedescribed below.

As described above, the processing region 42 is etched by the focusedion beam 21, the exposed cross-section 42 s is irradiated with theelectron beam 22, and the observation image and the EDS map of thecross-section 42 s are acquired. Next, the processing region 43 isetched by the focused ion beam 21, and the observation image of theexposed cross-section 43 s is acquired. Next, the processing region 44is etched by the focused ion beam 21, the exposed cross-section 44 s isirradiated with the electron beam 22, and the observation image of thecross-section 44 s is acquired. By repeatedly performing thecross-section processing and the cross-section observation (Cut&See),the plural observation images of the cross-sections along thepredetermined direction PD are acquired. By performing image processingof sequentially combining these plural observation images, athree-dimensional image of a predetermined region of the sample S can beacquired.

(First Embodiment of Cross-Section Processing-and-Observation Method)

Next, a method in which, based on the summary of the above-describedcross-section processing-and-observation method, cross-sectionprocessing-and-observation is performed while updating a conditionsetting of the cross-section exposure step and a condition setting ofthe cross-sectional image acquisition step to construct athree-dimensional image of an observation target will be described withreference to FIGS. 1, 2, and 4 to 9B. In the following embodiment, acase of setting two types of specific observation targets and performingcross-section processing-and-observation of a sample in which the twotypes of specific observation targets are present close to each other isassumed.

FIG. 4 illustrates a sample S including a specific material M1 and aspecific material M2 which are specific observation targets. Adeposition film (not illustrated) is formed on the sample S in advance,and a correction pattern T is formed on the deposition film to linearlyextend along the predetermined direction (processing progressiondirection) PD. This correction pattern T is formed by, for example,irradiation of the focused ion beam 21.

First, in the vicinity of a position where the specific material M1 andthe specific material M2 are assumed to be present, a slope-shapedprocessing groove 51 is formed by etching using the focused ion beam 21.Next, a condition setting for cross-section processing-and-observationis set. In the condition setting of the cross-section exposure step, inorder to detect the specific materials M1 and M2, the position and sizeof a processing region 52 are set at a slicing interval of D1 of, forexample, 50 nm. In addition, as the condition setting of thecross-sectional image acquisition step, the accelerating voltage of theelectron beam 22 is set as, for example, 5 kV. In addition, carbon andiron are set as constitutional elements of the specific materials. Inthe embodiment, it is assumed that the specific material M1 is carbonand the specific material M2 is iron.

When a cross-section is observed with the electron beam 22 which isaccelerated at an accelerating voltage of 5 kV, the penetration lengthof the electron beam 22 through the sample S is about 50 nm. Therefore,when the cross-section is irradiated with the electron beam 21 at theslicing interval D1 of 50 nm, the electron beam 22 is incident withinthe next slicing range, that is, within a range of the slicing intervalD1. Thus, when being present in this range, the specific material M1 andthe specific material M2 can be detected. As a result, even if the sizesof the specific material M1 and the specific material M2 are the slicinginterval D1 or less, the specific material M1 and the specific materialM2 can be detected with the cross-section processing-and-observation atthe slicing interval D1.

Next, a cross-section 52 s which is formed by slicing is irradiated withthe electron beam 22 to acquire a SEM observation image of thecross-section 52 s. In addition, an X-ray generated by irradiation ofthe electron beam 22 is detected by the EDS detector 18. At this time, acharacteristic X-ray of silicon, oxygen, aluminum, copper, or the likewhich is a material included in a device is detected from the sample Swhich is a semiconductor wafer. The image forming unit 23 forms an EDSmap, which is a material distribution in an irradiation region of theelectron beam 21, based on the irradiation position of the electron beam21 and the detected characteristic X-ray. Slicing and EDS map formingare repeatedly performed. When carbon as the specific material M1 oriron as the specific material M2 appears on the EDS map, conditions ofthe cross-section exposure step and conditions of the cross-sectionalimage acquisition step are updated.

For example, when a processing region 53 is sliced, carbon as thespecific material M1 is detected at a cross-section 53 s of theprocessing region 53. Here, conditions of the cross-sectional imageacquisition step are updated. For example, in order to observe thespecific material M1 in more detail to acquire a detailedthree-dimensional image, a minute region including the specific materialM1 is set in the cross-section s. A condition setting is set such thatonly the minute region including the specific material M1 can beobserved with a higher magnification than an observation magnificationof the entire cross-section s. As a result, the observation image of theentire cross-section s and the high-magnification observation image onlyfor the minute region including the specific material M1 are acquired.

The condition setting of the cross-sectional image acquisition stepincludes, for example, an accelerating voltage of the electron beam 21,a current value of the electron beam 21, an aperture value of an objectlens of the electron beam column 12, an astigmatism correction amount, abrightness of an observation image, a contrast, a magnification, animaging time of the observation image, the number of times of acquiringan observation image for each cross-section, a pixel size, and adetector used for acquiring an cross-sectional image. By updating theseconditions of the cross-sectional image acquisition step in thecross-section where the preset specific material is detected, theobservation image of the entire cross-section s and thehigh-magnification and high-resolution observation image only for theminute region including the specific material are acquired.

Next, in a state where the conditions of the cross-sectional imageacquisition step are updated, the slicing of processing regions 54 to 56and the acquisition of an observation image of a cross-section in eachprocessing region are performed along the predetermined direction PD.During this time, while the specific material M1 is detected, theobservation image of the entire cross-section s and the high-resolutionobservation image only for the minute region including the specificmaterial M1, which is observed with a higher magnification than anobservation magnification of the entire cross-section s, are acquired.

When slicing is further performed along the predetermined direction PD,iron as the specific material M2 is detected in, for example, across-section 57 s of a processing region 57. Here, conditions of thecross-sectional image acquisition step are updated, and conditions ofthe subsequent cross-section exposure step are updated.

For example, in order to observe the specific material M2 in more detailto acquire a detailed three-dimensional image, a minute region includingthe specific material M2 is set in the cross-section s. A conditionsetting is set such that only the minute region including the specificmaterial M2 can be observed with a higher magnification than anobservation magnification of the entire cross-section s. As a result,the observation image of the entire cross-section s, thehigh-magnification observation image only for the minute regionincluding the specific material M1, and the high-magnificationobservation image only for the minute region including the specificmaterial M2 are acquired.

The condition setting of the cross-sectional image acquisition stepincludes, for example, an accelerating voltage of the electron beam 21,a current value of the electron beam 21, an aperture value of an objectlens of the electron beam column 12, an astigmatism correction amount, abrightness of an observation image, a contrast, a magnification, animaging time of the observation image, the number of times of acquiringa observation image for each cross-section, and a pixel size. Byupdating these conditions of the cross-sectional image acquisition stepin the cross-section where the preset specific material is detected, theobservation image of the entire cross-section s and thehigh-magnification and high-resolution observation images only for theminute regions including the respective specific material are acquired.

FIG. 5 is a schematic diagram of observation images of a cross-section.In an example of the observation images of the cross-section illustratedin FIG. 5, observation images are acquired from two minute regions E1and E2 including specific observation targets under differentacquisition conditions from those of an observation image of the entirecross-section. For example, when the observation image of the entirecross-section is acquired with a low magnification, an SEM image isacquired from the minute region E1 with a medium magnification. Inaddition, by acquiring a BSE image, a composition distribution in theminute region E1 is obtained. On the other hand, when the observationimage of the entire cross-section is acquired with a low magnification,an SEM image is acquired from the minute region E2 with a highmagnification.

In this way, plural minute regions including respective plural specificmaterials are set in a cross-section exposed by slicing, differentcondition settings of the cross-sectional image acquisition step are setfor the individual minute regions. As a result, a highly accurateobservation image having a shape and a composition of each of presetarbitrary specific materials can be acquired. In addition, anobservation image is acquired from the entire cross-section exposed byslicing with, for example, a low magnification, and an observation imageis selectively acquired from only a minute region including each ofplural specific materials with a high magnification. As a result, ascompared to a case where an observation image is acquired from theentire cross-section with a high resolution, the highly accurate shapeand composition of a specific material can be effectively obtainedwithin a short period of time.

When the condition setting of the cross-sectional image acquisition stepis set, it is preferable that the type of an observation image of across-section be reflected on the setting value of the slicing intervalin the condition setting of the cross-section exposure step. That is,for example, when a SEM image is used as an observation image, thesetting value of the slicing interval is set to be an integer multipleof a resolution setting value of the SEM image. As a result, an errorbetween the slicing interval of the sample S and the resolution of theSEM image can be eliminated. That is, in the case of a three-dimensionalimage, the size of a voxel which is a pixel of the three-dimensionalimage can be clarified, and three-dimensional information can be moreaccurately displayed.

Regarding the setting of a minute region in one cross-section, twominute regions are set in the above-described example. However, bysetting three or more minute regions, different condition settings ofthe cross-sectional image acquisition step can be set for the individualminute regions.

When a continuous cross-section is processed by FIB, an image of thecorrection pattern T which is formed on the deposition film in advanceis acquired. For example, as illustrated in FIG. 6, when a cross-sectionof the sample S is formed by the focused ion beam 21, the FIB is alsoemitted onto the correction pattern T which is formed in the vicinity ofthe cross-section to acquire an image of the correction pattern T at thesame time. At this time, conditions of the cross-section exposure stepof the correction pattern T are updated such that the image of thecorrection pattern T is acquired with a higher magnification than thatof the SIM image acquired when the cross-section of the sample S isprocessed.

For example, the condition setting is performed such that themagnification of the observation image of the correction pattern T isfour times that of the SIM image acquired when the cross-section of thesample S is processed. As a result, the accuracy of the correctionpattern recognition can be made 4 times higher, and the accuracy ofprocessing can be improved. In this way, when the image of thecorrection pattern T is acquired, the magnification is set to be higherthan that of the SIM image acquired when the cross-section of the sampleS is processed. As a result, each cross-section can be formed by FIBbased on the correction pattern T with a higher accuracy than that ofdrift correction.

In addition, in a case where a three-dimensional image is constructed inthe subsequent step, when an observation image is acquired from across-section which is formed for each of processing regions, an imageof a correction pattern of electron beam which is formed outside anobservation region of the cross-section is acquired. For example, whenan observation image of a cross-section of the sample S which is formedby the focused ion beam 21 is acquired by irradiation of the electronbeam 22, the correction pattern of electron beam which is formed in thevicinity of the observation region is also irradiated with the electronbeam 22 to acquire an image of the correction pattern at the same time.At this time, conditions of the cross-sectional image acquisition stepof the correction pattern are updated such that the image of thecorrection pattern is acquired with a higher magnification than that ofthe observation image of the cross-section of the sample S.

For example, the condition setting is performed such that themagnification of the observation image of the correction pattern T isfour times that of the observation image of the cross-section of thesample S. As a specific example, if the visual field range of anobservation image of a cross-section of the sample S is 10 μM and thepixel size thereof is 10 nm, when the magnification of an observationimage of a correction pattern is four times that of the observationimage of the cross-section of the sample S, the visual field range is 25μm and the pixel size is 2.5 nm.

In this way, when the image of the correction pattern T is acquired, themagnification is set to be higher than that of the observation image ofthe cross-section of the sample S. As a result, when cross-sectionalimages of cross-sections can be combined based on the correction patternin the subsequent step, correction of the combining of thecross-sectional images can be performed. In particular, when ahigh-magnification observation image is acquired from only a minuteregion including a specific material under acquisition conditionsdifferent from those of an observation image of the entirecross-section, a three-dimensional image which includes the highresolution image of the minute region including the specific materialcan be constructed by acquiring an observation image of a correctionpattern with a high magnification according to the high magnification ofthe minute region.

After iron as the specific material M2 is detected in the EDS map,conditions of the cross-section exposure step are updated. Asillustrated in FIG. 7, in processing regions subsequent to theprocessing region 57 where the specific material M2 is detected, slicingis performed at a slicing interval D2 which is narrower than the slicinginterval D1 of the processing regions 52 to 57 of the sample S. Theslicing interval D2 is set as, for example, 5 nm.

The slicing interval is set to be an integer multiple of for example, aresolution setting value of the SEM image in the condition setting ofthe cross-sectional image acquisition step. As a result, an errorbetween the slicing interval of the sample S and the resolution of theSEM image can be eliminated.

The conditions of the cross-section exposure step are updated byupdating at least one of an accelerating voltage of the focused ion beam21, a current value of the focused ion beam 21, an irradiation range ofthe focused ion beam 21 in the sample, and a visual field range of thefocused ion beam 21.

After the conditions of the cross-section exposure step is updated andthe specific material M2 is detected, other cross-sections are sliced atthe slicing interval D2 which is narrower than the slicing interval D1by about 5 nm. Even if the size of the specific material M2 is, forexample, about 60 nm, 10 or more cross-sections Ms are formed from aminute region including the specific material M2, and observation imagesof the cross-sections Ms can be obtained. The minute region includingthe specific material M2 is set such that an observation image thereofis acquired with a higher magnification than an observation image of theentire cross-section by updating the conditions of the cross-sectionalimage acquisition step. Therefore, a three-dimensional image having ahigh-resolution image of the specific material M2 can be constructed byupdating the conditions of the cross-section exposure step and theconditions of the cross-sectional image acquisition step and acquiringan observation image of the above-described correction pattern T with ahigher magnification than that of the observation image of the entirecross-section.

In the above-described embodiment, after the specific material M2 isdetected, other cross-sections are sliced in the same slicing rangewhile reducing the slicing interval. However, for example, aconfiguration can also be adopted in which: in the case of the specificmaterial M1, only the presence thereof needs to be confirmed; and in thecase of the specific material M2, when it is desired to acquire athree-dimensional image of the entire shape thereof, only a minuteregion including the specific material M2 is sliced.

In the embodiment illustrated in FIG. 8, in processing regionssubsequent to the processing region 57 where the specific material M2 isdetected, the conditions of the cross-section exposure step are updated,in which the irradiation region of the focused ion beam 21 in the sampleS is limited to the minute region including the specific material M2 andslicing is performed at the slicing interval D2 which is narrower thanthe slicing interval D1.

In this way, by limiting the processing region of the sample S to theminute region including the specific material M2, a processing width W1of the processing regions 52 to 57 is larger than a processing width W2of processing regions subsequent to the processing regions 52 to 57.Therefore, the processing area is narrowed and the time required forprocessing is reduced. In addition, the acquisition range of anobservation image in each cross-section is narrowed and the timerequired for acquiring a cross-sectional image is reduced. As a result,cross-section processing-and-observation can be efficiently performedwithin a short period of time.

A configuration can also be adopted in which the irradiation range ofthe focused ion beam 21 is limited to both a minute region including thespecific material M1 and a minute region including the specific materialM2, the plural minute regions are sliced, and an observation image isacquired from each of cross-sections thereof.

When the specific observation target (specific material) is detected,the condition setting of the cross-section exposure step and thecondition setting of the cross-sectional image acquisition step areupdated, and the cross-section processing-and-observation is performed.The cross-section processing-and-observation may be performed until thecross-section processing-and-observation of the entire preset range iscompleted. However, for example, the condition setting of thecross-section exposure step may be set such that the cross-sectionprocessing-and-observation ends at a position where the specificmaterial M1 is not detected anymore or at a position where the specificmaterial M2 is not detected anymore.

FIGS. 9A and 9B illustrate setting examples of an end condition of thecross-section exposure step. For example, in an example illustrated inFIG. 9A, the end condition of the cross-section exposure step is aposition where all the preset specific observation targets (specificmaterials) M11 to M14 are not detected anymore. In this setting example,the specific examples M11 to M14 are detected based on the EDS map, theEBSD map, the contrast of the SEM image, and the like, and thecross-section exposure step ends at a slicing position where all thespecific materials M11 to M14 are not detected anymore in across-section.

In addition, in an example illustrated in FIG. 9B, plural types ofspecific observation targets (specific materials) are set, the thresholdnumber of the specific materials detected is set to 4, and the endcondition of the cross-section exposure step is a position where thenumber of the specific materials detected is less than 4 after a slicingposition where the number of the specific materials detected is 4 ormore. In this setting example, based on the EDS map, the EBSD map, thecontrast of the SEM image, and the like, the cross-section exposure stepends at a slicing position where the number of the specific materialsdetected is less than 4.

In this way, slicing is not performed in the entire preset region, andthe cross-section exposure step is ended according to the detectionstate of the specific material based on the EDS map, the EBSD map, thecontrast of the SEM image, and the like. As a result, the desiredspecific observation target (specific material) can be efficientlyobserved within a short period of time.

From the observation images of the cross-sections acquired as above, athree-dimensional image is constructed by the three-dimensional imageconstruction unit 37. The three-dimensional image construction unit 37acquires the plural cross-sectional images accumulating in theobservation image storage unit 35 and arranges the pluralcross-sectional images to be substantially parallel to each other at aninterval corresponding to the slicing interval. At this time, driftcorrection is performed based on the correction pattern T which isacquired at the same time with the acquisition of the individualobservation images. Spaces between the arranged observation images arecomplemented to construct a three-dimensional image.

The obtained three-dimensional image is constructed based on theobservation images of the cross-sections acquired by updating theconditions of the cross-section exposure step and the conditions of thecross-sectional image acquisition step according to the specificmaterials. In addition, during the cross-section processing and duringthe construction, drift correction is performed with reference to thecorrection pattern which is acquired at a high magnification. Therefore,a highly accurate three-dimensional image which is close to the actualshape can be obtained. Accordingly, a three-dimensional image of aminute defect or structure included in the sample S can be accuratelyobtained within a short period of time.

FIG. 10 is illustrates an example of a three-dimensional image which isconstructed using the cross-section processing-and-observation methodaccording to the present invention. According to the constructionexample of the three-dimensional image illustrated in FIG. 10, a sampleincludes two specific observation targets (specific materials) M21 andM22. Observation images of cross-sections accumulate at a relativelylarge slicing interval until the specific material M21 is detected.After the specific material M21 is detected, observation images ofcross-sections accumulate at a small slicing interval. In addition, anobservation image is acquired from a minute region M21E including thespecific material M21 with a higher magnification than that of the otherregions. Further, a minute region M22E including the specific materialM22 is set halfway, and an observation image is also acquired from thisregion with a high magnification. Cross-section processing ends at aposition where the specific material M22 is not detected anymore. Inthis way, while constructing a highly accurate three-dimensional imageIm of the specific materials M21 and M22, the slicing interval of aregion including no specific material is increased or slicing ends. As aresult, the highly accurate three-dimensional image Im including thespecific materials M21 and M22 can be obtained within a short period oftime.

(Second Embodiment of Cross-Section Processing-and-Observation Method)

Next, a cross-section processing-and-observation method according to asecond embodiment of the present invention will be described in whichthe cross-section processing-and-observation method according to thefirst embodiment is automatically performed. FIG. 11 is a flowchartillustrating the cross-section processing-and-observation method.Condition settings of the cross-section processing-and-observation areset (S1). Here, as the condition setting of the cross-section exposurestep, initial setting values for an accelerating voltage of the focusedion beam 21, a current value of the focused ion beam 21, an irradiationrange of the focused ion beam 21 in the sample S, a visual field rangeof the focused ion beam 21, and the like are input. In addition, as thecondition setting of the cross-sectional image acquisition step, initialsetting values for an accelerating voltage of the electron beam 21, acurrent value of the electron beam 21, an aperture value of an objectlens of the electron beam column 12, an astigmatism correction amount, abrightness of an observation image, a contrast, a magnification, animaging time of the observation image, the number of times of acquiringan observation image for each cross-section, a pixel size, and the likeare input. Further, the type of the element included in the specificobservation target and the shape of the specific material are input. Inaddition, an end condition of the cross-section exposure step, forexample, the number of the specific materials detected is input. Theconditions of the cross-section exposure step and the conditions of thecross-sectional image acquisition step are updated when the specificmaterial is detected after the start of processing.

Next, cross-section processing-and-observation is performed (S2). Apreset processing region is irradiated with a focused ion beam, andslicing is performed along a predetermined direction a cross-sectionformed by slicing is irradiated with an electron beam to acquire anobservation image of the cross-section. An X-ray generated from thecross-section is detected by the EDS detector.

Whether or not a processing end condition is satisfied is determined foreach cross-section processing-and-observation (S3). The processing endcondition is input in advance. For example, as illustrated in FIG. 9,the processing end condition is the slicing position where all thespecific materials are not detected anymore or the slicing positionwhere the number of the specific materials detected falls below apredetermined value.

When the cross-section processing-and-observation is continued withoutending slicing, the presence of the preset specific material is detected(S4). For example, when the specific material is detected based on theEDS map, the conditions of the cross-sectional image acquisition stepare updated (S5). For example, one or plural minute regions includingthe specific materials may be set for each cross-section. Differentobservation magnifications, observation ranges, composition analysissettings, and the like are set for the individual minute regions.

Next, the conditions of the cross-section exposure step are updated(S6). For example, according to the update of the conditions of thecross-sectional image acquisition step, a setting of limiting theslicing region to be reduced according to the individual minute regionsor a setting of reducing the slicing interval according to the size ofthe specific material is set.

The cross-section processing-and-observation is repeatedly performedwhile reflecting the update of the conditions of the cross-sectionalimage acquisition step and the update of the conditions of thecross-section exposure step (S2). When it is determined that theprocessing end condition is satisfied, the cross-sectionprocessing-and-observation ends at this time.

As described above, by automatically performing the cross-sectionprocessing-and-observation method according to the first embodimentbased on the previously input setting values, observation images ofdesired cross-sections or a three-dimensional image constructed based onthe observation images can be efficiently and accurately acquired. Thiscontrol is performed by, for example, the controller 25 illustrated inFIG. 1.

Hereinafter, the cross-section processing-and-observation apparatus andthe cross-section processing-and-observation method according to thepresent invention have been described in detail. However, the presentinvention is not limited to the above-described embodiments unlessspecified otherwise.

For example, the conditions of the cross-section exposure step includeall the condition settings of the cross-sectionprocessing-and-observation apparatus which are necessary to arbitrarilyupdate the slicing interval and the slicing range of the sample. Inaddition, the conditions of the cross-sectional image acquisition stepinclude all the condition settings of the cross-sectionprocessing-and-observation apparatus which are necessary to arbitrarilyupdate the range of an observation image of a cross-section, the numberof minute regions set, the magnification of an observation image, andthe like.

In addition, as an example of a detection method of the specificobservation target (specific material), EDS is mainly used. However, inaddition to EDS, various detection methods such as EBSD, a method ofdetecting a contrast change by an SEM image, and a method of detecting adifference from a comparison with a reference image can be adopted, andthe detection method is not particularly limited.

In addition, the detection of the specific observation target is notlimited to the detection of the element. As the specific observationtarget, a molecular structure, a crystal structure, an external shape,or the like can be detected.

What is claimed is:
 1. A cross-section processing-and-observation methodcomprising: a cross-section exposure step of irradiating a sample with afocused ion beam to expose a cross-section of the sample; across-sectional image acquisition step of irradiating the cross-sectionwith an electron beam to acquire a cross-sectional image of thecross-section; a step of repeatedly performing the cross-sectionexposure step and the cross-sectional image acquisition step along apredetermined direction of the sample at a setting interval to acquire aplurality of cross-sectional images of the sample; and a specificobservation target detection step of detecting a predetermined specificobservation target from the cross-sectional image acquired at thecross-sectional image acquisition step; wherein in the specificobservation target detection step, after a predetermined specificobservation target is detected, the setting interval of thecross-section exposure step is set to be shorter than that before thespecific observation target is detected.
 2. The cross-sectionprocessing-and-observation method according to claim 1, wherein thesetting interval is equal to or an integer multiple of a pixel size ofthe cross-sectional image, or the pixel size is an integer multiple ofthe setting interval.
 3. The cross-section processing-and-observationmethod according to claim 1, wherein plural types of the specificobservation targets are set, and different condition setting of thecross-section exposure step and different condition setting of thecross-sectional image acquisition step are set for individual regionswhere the respective specific observation targets are detected.
 4. Thecross-section processing-and-observation method according to claim 3,wherein when the condition setting of the cross-section exposure stepand the condition setting of the cross-sectional image acquisition stepare set, the setting interval is equal to or an integer multiple of apixel size of the cross-sectional image.
 5. The cross-sectionprocessing-and-observation method according to claim 1, wherein in thespecific observation target detection step, an EDS measurement or anEBSD measurement of the cross-section is performed.
 6. The cross-sectionprocessing-and-observation method according to claim 1, wherein thespecific observation target detection step includes observing a contrastchange of a cross-sectional image obtained in the cross-sectional imageacquisition step.
 7. The cross-section processing-and-observation methodaccording to claim 3, wherein the condition setting of the cross-sectionexposure step includes at least one of an accelerating voltage of thefocused ion beam, a current value of the focused ion beam, anirradiation range of the focused ion beam in the sample, and a visualfield range of the focused ion beam.
 8. The cross-sectionprocessing-and-observation method according to claim 1, wherein thespecific observation target detection step is performed once while thecross-sectional image acquisition step is performed multiple times. 9.The cross-section processing-and-observation method according to claim1, wherein in the specific observation target detection step performedafter the specific observation target is detected, cross-sectionprocessing-and-observation is not performed on other portions of thesample when the specific observation target is not detected anymore. 10.The cross-section processing-and-observation method according to claim1, further comprising a step of forming a correction mark by irradiationof the focused ion beam, wherein in the cross-section exposure step, animage of the correction mark is acquired with a higher magnificationthan a visual field range of the focused ion beam among the conditionsof the cross-section exposure step.
 11. The cross-sectionprocessing-and-observation method according to claim 1, furthercomprising a step of forming a correction mark by irradiation of thefocused ion beam, wherein in the cross-sectional image acquisition step,when the cross-sectional image is acquired, an image of the correctionmark is acquired at the same time with a higher magnification than themagnification of a cross-section observation region observed by theelectron beam.
 12. A cross-section processing-and-observation apparatuscomprising: a sample stage on which a sample is to be placed; a focusedion beam column configured to irradiate the sample with a focused ionbeam; an electron beam column configured to irradiate the sample with anelectron beam; one of a secondary electron detector and a backscatteredelectron detector configured to detect one of secondary electrons andbackscattered electrons generated from the sample; and a control unitconfigured to repeatedly perform a cross-section exposure step in whichthe sample is irradiated with a focused ion beam emitted from thefocused ion beam column to expose a cross-section of the sample, and across-sectional image acquisition step in which the cross-section isirradiated with an electron beam emitted from the electron beam columnto acquire a cross-sectional image of the cross-section along apredetermined direction of the sample at a setting interval; wherein thecontrol unit is further configured to periodically perform a specificobservation target detection step of detecting a predetermined specificobservation target from the cross-sectional image acquired at thecross-sectional image acquisition step; and wherein in the specificobservation target detection step, after a predetermined specificobservation target is detected, the setting interval of thecross-section exposure step is set to be shorter than that before thespecific observation target is detected.
 13. The cross-sectionprocessing-and-observation apparatus according to claim 12, wherein thecontrol unit controls the setting interval to be equal to or an integermultiple of a pixel size of the cross-sectional image or controls thepixel size to be an integer multiple of the setting interval.